Collaborative Research: Fundamental Properties of Local Subdwarfs

关于银河系形成和演化的许多悬而未决的问题需要更好地了解银河系光晕和厚盘中局部贫金属亚矮星的运动学和化学富集型式，以及这些与球状星团恒星的比较。即使经过最近的几次努力，目前的样本仍不能充分覆盖球状星团中所见的金属性和运动学的范围，而对本地贫金属巨星的观测给出了诱人的证据，证明了本地晕星和球状星团中的相同金属之间的显著差异。这个项目将通过获得最近对贫金属星的调查中确定的大约150颗亚矮星的精确和自洽的温度、变红和成分测量来改善观测情况。还将有新的理论努力来探索主序光度与详细的恒星化学成分和经常被忽视的物理(如氦扩散和旋转)的相关性。该项目还将提供关于光晕和厚盘贫金属尾巴的运动学和恒星形成历史的宝贵信息，查明在丰度模式和运动学上与球状星系星匹配的亚矮星样本，并改进球状星系团主要序列的温度和丰度尺度，以便与巨型分支上的光谱测定进行比较。还将对球状星团的相对年龄和绝对年龄进行系统的研究，重点是减少理论平面上的误差。重要的是，该项目将使社区能够充分利用未来的名气和SIM卫星任务，这将测量样本中的亚矮星的准确视差，从而产生球状星团的主序光度的绝对校准以及此后它们的距离。目前的距离估计只有10%-15%，导致年龄误差约30%，与恒星演化理论的预测相比，不足以可靠地探索球状星团系统中的年龄扩散，甚至不足以设定宇宙年龄的下限。

AST 0205789TerndrupMany outstanding issues concerning the formation and evolution of the Milky Way require improvedknowledge of the kinematics and chemical enrichment patterns of local metal-poor subdwarfs in theGalaxy's halo and thick disk, and how these compare to globular cluster stars. Even after several recentefforts, current samples do not adequately cover the range of metallicities and kinematics seen in globularclusters, while observations of local metal-poor giants give tantalizing evidence of significant differencesbetween local halo stars and those in globular clusters of the same metallicity.This project will improve the observational situation by obtaining accurate and self-consistentmeasures of temperature, reddening, and composition for a critically selected sample of approximately150 subdwarfs identified in recent surveys for metal-poor stars. There will also be new theoretical effortsto explore the dependence of the main-sequence luminosity on detailed stellar chemical composition andon often-neglected physics such as helium diffusion and rotation. This project will also yield valuableinformation on the kinematics and star formation history of the halo and the metal-poor tail of the thickdisk, identify samples of subdwarfs that are well matched in abundance patterns and kinematics toglobular cluster stars, and improve the temperature and abundance scales of globular cluster mainsequences for comparison to spectroscopic determinations on the giant branch. There will also be asystematic study of the relative and absolute ages of globular clusters, with a focus on reducing the errorsin the theoretical plane.Importantly, this project will enable the community to take full advantage of the future FAME andSIM satellite missions, which will measure accurate parallaxes for the subdwarfs in the sample andthereby yield the absolute calibration of the main-sequence luminosity for globular clusters and hencetheir distances. Current distance estimates are only good to 10 - 15%, resulting in age errors of about30%, insufficient to reliably explore the age spread in the globular cluster system or even set lower limitsto the age of the Universe by comparison with the predictions of stellar evolution theory.